1. More on Ionic and Covalent Compounds

2. What is a compound?
A chemical made of two or more atoms bonded together in a set ratio

3. Intramolecular forces
Forces that hold the atoms in a compound together (aka chemical bonds)
Can be:
Ionic
Covalent
Metallic

4. Ionic Compounds (salts)
Formed when valence electrons are transferred amongst atoms. This creates cations and anions which then attract each other.

5. Naming Ionic Compounds
State the name of the cation first
If it is a transition metal with more than one oxidation state, include the charge with roman numerals.
Examples: Na = sodium
Cs = cesium
Fe = iron (II) or iron (III) *depending on what it is bonded to

6. If the anion is an element, you write the beginning of its name, but change the ending to “–ide”
Examples:
Na2O = sodium oxide (note that the “2” does not affect the name)
KCl = potassium chloride

7. If the anion is more than one element, you simply write the name of the polyatomic ion.
Examples:
NaNO3 = sodium nitrate
CsClO3 = cesium chlorate
Ba3(PO4)2 = barium phosphate

8. Writing Formulas for Ionic Compounds
For a compound to be stable, the overall charge must equal zero.
So, figure out the charge of the cation (always positive) and the charge of the anion (always negative) and determine how many of each you need to balance the compound.

9. Examples Magnesium oxide Mg = 2+ O = 2- MgO Beryllium cyanide
Be=2+ CN = 1-
Be(CN)2
Lead (II) nitride
Pb = 2+ N = 3-
Pb3N2

10. Covalent Compounds (molecules)
Formed when atoms share one or more pairs of valence electrons.

11. Types of covalent bonds
Nonpolar
Electrons are being shared evenly.
Polar
Electrons are spending more time with one type of atom than the other.
**Which type forms is determined by the electronegativity of the involved atoms (how strongly an atom pulls electrons toward itself)

13. Polar Covalent
If two atoms have a larger difference in electronegativity, then they will share electrons unevenly.
For example, oxygen has an electronegativity of 3.0, while hydrogen has an electronegativity of Since oxygen is more electronegative, it will get to spend more time with the shared electrons.

14. Nonpolar covalent
If two atoms have a very similar electronegativity, then they will share electrons evenly.
For example, carbon has an electronegativity of 2.5, while selenium has an electronegativity of These are pretty close, so the atoms share evenly.

15. Electronegativity and Bond Type
Electronegativity Difference
Type of Bond Formed
0.0 to 0.2
nonpolar covalent
0.3 to 1.4
polar covalent
> 1.5
ionic
**I have checked several resources, and each lists a slightly different set of numbers. As best I can tell, these are arbitrarily chosen and should be used only as a guideline.

16. Naming Covalent Compounds
As before, you use the full name of the first element and change the ending of the second element to “- ide.”
We use prefixes to indicate the number of each type of atom involved.

17. Memorize for quiz Prefix number indicated mono- 1 di- 2 tri- 3 tetra-4
penta- 5
hexa- 6
hepta- 7
octa- 8
nona- 9
deca- 10

18. Examples C3H8 = tricarbon octahydride N2O = dinitrogen monoxide
H2O = dihydrogen monoxide
H2O2 = dihydrogen dioxide
P4O6 = tetraphosphorus hexaoxide

19. The exception
If there is only one atom of the first chemical, we leave out the “mono-”.
Examples:
CO = Carbon monoxide
CO2 = Carbon dioxide

20. Diatomic Molecules
There are certain elements that are only found in nature as a covalent molecule made of two identical atoms. All of them are gases at room temperature.
BrINClHOF
Bromine – Br2 Hydrogen –H2
Iodine - I2 Oxygen – O2 Nitrogen - N2 Fluorine – F2
Chlorine- Cl2